In the glass industry today the most common glass container manufacturing machine is the Hartford type "I.S." machine. It is estimated that in the United States alone, there are over six thousand "I.S." sections in daily operation. This machine is described in Ingle U.S. Pat. Nos. 1,843,160 and 1,911,119.
A basic "I.S." eight-section machine today costs several hundred thousand dollars. An important advantage of the present invention is that it is applicable to the existing production facilities of the industry.
In the original disclosure of the I.S. machine, the machine was intended to make glass containers by the well-known "blow and blow" process. Subsequently, Rowe U.S. Pat. No. 2,289,046 disclosed the "62" process which could be applied to the basic machine to enable it to make containers by the "press and blow" process which is the preferred method of manufacturing wide mouth ware or jars. This development enabled the glass industry to use one machine for all types of ware instead of having a "narrow neck" machine like the Owens or Lynch machines for making bottles and a "wide-mouth" machine like the Miller machine for making jars.
The present invention relates primarily to the manufacture of glass containers on the I.S. machine by the well-known "blow and blow" process although there are some instances where it can also be used to advantage in the manufacture of glass containers in the I.S. machine using the "press and blow" process. Although minor variations to the process exist in the industry, the following discussion describes generally the steps which are most common. A gob of molten glass is delivered into an inverted blank mold at the bottom of which is situated a neck ring and a plunger. The gob is blown down into the cavity with compressed air to insure the complete filling of the neck ring. The plunger is then receded, a baffle plate closes the top end of the blank cavity, and compressed air is applied through the orifice created by the withdrawal of the plunger, thereby expanding the glass into intimate contact with the interior surfaces of the blank mold and baffle plate. The glass-to-mold contact is continued long enough to create an "enamel" skin on the outer surface of the resulting glass parison.
The baffle plate is then removed and the blank mold is slightly disengaged from the parison so that the parison is held in a vertical position supported only by the neck ring. At this time, the parison starts to "reheat" which refers to the flow of heat from the interior glass to the outer surfaces of the parison and to the heat reflected from the interior surface of the blank mold to the outer surface of the parison. The step of reheating the parison plays an important role in improving the strength of the final glass bottle. Following this, the neck ring and parison are transferred and inverted to the blow mold position. The blow mold closes around the parison as the neck ring releases its hold, and the parison becomes supported at the top of the blow mold by a finish ring or bead located just below the finish of the parison. The parison, of course, continues to reheat during its transfer to and positioning in the blow mold until the time it is expanded into contact with the interior wall of the blow mold.
After its suspension in the blow mold, compressed air and/or vacuum are applied, at the proper time, to expand the parison to the interior contours of the blow mold. The cooling contact between the blown glass bottle and the blow mold is maintained until the bottle assumes a sufficient degree of rigidity to be capable of standing on its own. Then the blow mold is opened and the glass bottle is removed therefrom and transferred to a cooling plate or conveyor.
As glass bottles have been designed for lighter weights and thinner walls, the length of time required to blow and cool the bottle in the blow mold has decreased significantly. Therefore, in order to maintain the blank side time in the proper relation to the blow side time, it has been necessary to reduce the time available for reheating the parison.
In the ideal production of thin-walled containers, the interval for reheating prior to blowing must exceed a predetermined minimum period of time in order to insure equalization of temperatures in all zones of the parison and to thus achieve uniform viscosity prior to final expansion. Reheating of the parison walls proceeds from the interior zone toward the exterior and, therefore, this step cannot be speeded up appreciably by auxiliary equipment. It also requires more time on containers where the parison has been formed by the "blow and blow" process than as those where the parison has been formed by the "press and blow" process because, in the former there is no plunger contact to cool the interior wall of the parison as there is in the latter process.
Many inventors, recognizing the importance of the "reheat" have proposed means to increase it. These include Wadman U.S. Pat. No. 2,084,285, Wadman U.S. Pat. No. 2,151,876, Becker U.S. Pat. No. 3,622,304, Foster U.S. Pat. No. 4,009,016 and Zappia U.S. Pat. No. 4,058,388. Because none of these disclosures is applicable to the basic "I.S." machine they have not met with commercial acceptance.
It is important to keep the proper relationship between the blank side time and the blow side time to maintain a proper amount of reheating for the parison. In an attempt to improve the reheating time for the parisons additional blow molds have been provided so that the parisons can have additional reheat time without slowing down the parison forming or bottle forming process. The additional blow molds have been added to the bottle forming machine in usually one of two ways in the prior art. An additional set of blow molds can be added to one side of the parison forming equipment so that the parisons can alternately be supplied to each set of horizontally separated blow molds. (U.S. Pat. No. 3,216,813 is one example of this type of prior art system). The additional blow molds add a great deal of width to the bottle forming machine and require an additional parison transfer mechanism to service the additional blow molds. Such a mechanism requires a complete revamping of the forming stations and cannot be used with the standard I.S. machine.
The other prior art solution is to place two sets of blow molds on a horizontally reciprocating mechanism that alternately moves a blow mold set into position to receive parisons (U.S. Pat. No. 2,151,876 is one example of this type of prior art system). Once the first set of blow molds receives parisons the molds are horizontally translated and the second set of blow molds moves into position to receive parisons. The arrangement allows the parisons to have adequate reheat time while the parisons are being transferred to the blow molds and before the parisons are blown or expanded in the blow molds. However, the horizontal movement of the blow molds can cause the parisons to deform or move in the blow molds. Any such movement of the molten glass can produce non-uniformities in the parison that create non-uniformities in the finished blown bottle. Also the parison can deform to an extent, during the horizontal movement, to cause the parisons to contact the surface of the blow molds. Once the parisons contact the surface of the molds heat transfer occurs between the portion of the parison and the mold. The transfer disrupts the reheating of the parison in the area where the parison is in contact with the mold and creates a non-uniform reheating of the parison. The non-uniform reheating of the parison can create weak spots or defects in the finished bottle. The transfer of the parisons from the parison forming molds to the blow molds can also cause the parisons to deform or become off center. The subsequent horizontal movement of the blow molds will tend to magnify any such defects in the parisons and result in unsatisfactory bottles. Accordingly, the prior art solutions to the reheat problems have proven to be inadequate and not adaptable to present machines.
A substantial advantage of the present invention is that it is designed to be used with the Hartford type I.S. bottle forming machines. The Hartford type I.S. machine forming section has a width of under two (2) feet and bottle production facilities are designed to take maximum advantage of this width. The vertically reciprocating blow molds of the present invention can be added to the Hartford type I.S. machine without increasing the width of the bottle forming station of the machine. Thus, the present invention can be used to increase production rate in a bottle forming facility by adding the invention to standard bottle forming machinery.